Web media moving apparatus

ABSTRACT

An apparatus for moving a continuous web of print media includes a roller having an axis of rotation. The roller includes a pattern of recesses and ridges positioned along the axis of rotation of the roller. A second section of the roller is located between a first section of the roller and a third section of the roller as viewed along the axis of rotation. The roller includes a profile as viewed along the axis of rotation in which the diameter of the ridges located in the first section of the roller and the diameter of ridges located in the third section of the roller are greater than the diameter of the ridges located in the second section of the roller.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly-assigned, U.S. patent application Ser. No.______ (Docket K000158), entitled “WEB MEDIA MOVING METHOD”, Ser. No.______ (Docket K000159), entitled “PRINTING SYSTEM INCLUDING WEB MEDIAMOVING APPARATUS”, and Ser. No. ______ (Docket K000160), entitledPRINTING METHOD INCLUDING WEB MEDIA MOVING APPARATUS″, all filedconcurrently herewith.

FIELD OF THE INVENTION

This invention relates generally to a printing system for printing on aweb of print media, and in particular to an apparatus for moving the webof print media through the printing system.

BACKGROUND OF THE INVENTION

Some digital printing systems and processes, for example, inkjetprinting systems and processes introduce significant moisture contentduring operation, particularly when the system is used to print multiplecolors on a print media. Due to its moisture content, the print mediaexpands and contracts in a non-isotropic manner often with significanthysteresis. The continual change of dimensional characteristics of theprint media often adversely affects image quality. Although drying isused to remove moisture from the print media, drying too frequently, forexample, after printing each color, also causes changes in thedimensional characteristics of the print media that often adverselyaffects image quality.

During an inkjet printing process, as the print media absorbs thewater-based inks applied to it, the print media desires to expand. Whenthe direction of expansion is in a direction that is perpendicular tothe direction of media travel, it is often referred to as expansion inthe cross-track direction. For example, when the print media wrapsaround a roller of an inkjet printing system, the outer, typicallyunprinted, edges of the print media remain attached to the rolleralthough the remaining typically printed portions of the print mediaexpand outwardly. The outward expansion, commonly referred to asbuckling, of the print media in the cross-track direction between thefirmly attached outer edges of the print media creates lengthwiseripples or wrinkles in the print media. Wrinkling of the print mediaduring the printing process often leads to permanent creases forming inthe print media which ultimately affects image quality.

As such, there is an ongoing need to provide digital printing systemsand processes with the ability to effectively handle print mediaexpansion associated with the absorption of water by the print media.

SUMMARY OF THE INVENTION

According to an aspect of the invention, an apparatus for moving acontinuous web of print media includes a roller having an axis ofrotation. The roller includes a pattern of recesses and ridgespositioned along the axis of rotation of the roller. A second section ofthe roller is located between a first section of the roller and a thirdsection of the roller as viewed along the axis of rotation. The rollerincludes a profile as viewed along the axis of rotation in which thediameter of the ridges located in the first section of the roller andthe diameter of ridges located in the third section of the roller aregreater than the diameter of the ridges located in the second section ofthe roller.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description of the example embodiments of the inventionpresented below, reference is made to the accompanying drawings, inwhich:

FIG. 1 is a schematic side view of a digital printing system accordingto an example embodiment of the present invention;

FIG. 2 is an enlarged schematic side view of media transport componentsof the digital printing system shown in FIG. 1;

FIG. 3 is a schematic side view of a large-scale two-sided digitalprinting system according to another example embodiment of the presentinvention;

FIG. 4 is a schematic side view of a digital printing system accordingto another example embodiment of the present invention;

FIG. 5 is a schematic side view of an example embodiment of the presentinvention;

FIG. 6 is a schematic side view of another example embodiment of thepresent invention;

FIG. 7 is a schematic side view of another example embodiment of thepresent invention;

FIG. 8 is a schematic side view of another example embodiment of thepresent invention; and

FIG. 9 is a schematic side view of another example embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The present description will be directed in particular to elementsforming part of, or cooperating more directly with, apparatus inaccordance with the present invention. It is to be understood thatelements not specifically shown or described take various forms wellknown to those skilled in the art. In the following description anddrawings, identical reference numerals have been used, where possible,to designate identical elements.

The example embodiments of the present invention are illustratedschematically and not to scale for the sake of clarity. One of theordinary skills in the art will be able to readily determine thespecific size and interconnections of the elements of the exampleembodiments of the present invention.

In the context of the present disclosure, the term “continuous web ofprint media” relates to a print media that is in the form of acontinuous strip of media as it passes through the printing system froman entrance to an exit thereof. The continuous web of print media itselfserves as the receiving print medium to which one or more printing inkor inks or other coating liquids are applied in non-contact fashion.This is distinguished from various types of “continuous webs” or “belts”that are actually transport system components rather than receivingprint media and that are typically used to transport a cut sheet mediumin an electrophotographic or other printing system. The terms “upstream”and “downstream” are terms of art referring to relative positions alongthe transport path of a moving web; points on the web move from upstreamto downstream.

Generally described, an apparatus and method of moving a web of printmedia includes a roller that rotates about an axis of rotation as theprint media makes contact with and wraps around a portion of the rolleras the print media moves past the roller. The roller includes a patternof recesses and ridges positioned along the axis of rotation that helpcompensate for cross track expansion of the print media caused by theabsorption of water-based ink that is applied to the print media in theprint zone. The recesses and ridges also help to reduce the likelihoodof the print media wrinkling as the print media wraps around roller andmoves through printing system.

The printing system and method including the web moving apparatus areparticularly well suited for printing devices that provide non-contactapplication of ink, typically water based ink, or other colorant onto acontinuously moving web of print media. The printhead of the printingsystem selectively moistens at least some portion of the media as itcourses through the printing system, but without the need to makecontact with the print media.

Example embodiments of the print media web moving apparatus aredescribed below with reference to FIGS. 5-8. Example embodiments ofprinting systems including one or plurality of print media web movingapparatus are described below with reference to FIGS. 1-4. When includedin one of the printing systems described with reference to FIG. 2 or 3,print media web moving apparatus is typically located in one or both ofroller positions G or M. When included in the printing system describedwith reference to FIG. 4, print media web moving apparatus is typicallylocated in roller position M.

The digital printing system can also include components for drying orcuring of the printing fluid on the media; for inspection of the media,for example, to monitor and control print quality; and various otherfunctions. The digital printing system receives the print media from amedia source, and after acting on the print media conveys it to a mediareceiving unit. The print media is maintained under tension as it passesthrough the digital printing system, but it is not under tension as itis received from the media source.

The printing systems described with reference to FIGS. 1-4 includefeatures and principles of exact constraint for transportingcontinuously moving web print media past one or more digital printheads,such as inkjet printheads. The apparatus for moving a web of printmedia, however, works equally well in other types of print mediatransport systems.

Referring to the schematic side view of FIG. 1, there is shown a digitalprinting system 10 for continuous web printing according to oneembodiment. A first module 20 and a second module 40 are provided forguiding continuous web media that originates from a source roller 12.Following an initial slack loop 52, the media that is fed from sourceroller 12 is then directed through digital printing system 10, past oneor more digital printheads 16 and supporting printing system 10components. First module 20 has a support structure, shown in moredetail subsequently, that includes a cross-track positioning mechanism22 for positioning the continuously moving web of print media in thecross-track direction, that is, orthogonal to the direction of traveland in the plane of travel. In one embodiment, cross-track positioningmechanism 22 is an edge guide for registering an edge of the movingmedia. A tensioning mechanism 24, affixed to the support structure offirst module 20, includes a structure that sets the tension of the printmedia.

Downstream from first module 20 along the path of the continuous webmedia, second module 40 also has a support structure, similar to thesupport structure for first module 20. Affixed to the support structureof either or both the first or second module 20 or 40 is a kinematicconnection mechanism that maintains the kinematic dynamics of thecontinuous web of print media in traveling from the first module 20 intothe second module 40. Also affixed to the support structure of eitherthe first or second module 20 or 40 are one or more angular constraintstructures 26 for setting an angular trajectory of the web media.

Still referring to FIG. 1, printing system 10 optionally also includes aturnover mechanism 30 that is configured to turn the media over,flipping it backside-up in order to print on the reverse side. The printmedia then leaves the digital printing system 10 and travels to a mediareceiving unit, for example, a take-up roll 18. A take-up roll 18 isthen formed, rewound from the printed web media. The digital printingsystem can include a number of other components, including multipleprint heads and dryers, for example, as described in more detailsubsequently. Other examples of system components include web cleaners,web tension sensors, and quality control sensors.

A support structure 28 provides a supporting frame for mountingcomponents within module 20. Similarly, a support structure 48 providesa supporting frame for mounting components within module 40. Acontinuous web of print media 60 moves through printing system 10beginning at the source roller 12 and ending at the take-up roll 18.

The schematic side view diagram of FIG. 2 shows, at enlarged scale fromthat of FIG. 1, the media routing path through modules 20 and 40 in oneembodiment. Within each module 20 and 40, in a print zone 54, each printhead 16 is followed by a dryer 14.

Table 1 that follows identifies the lettered components used for webmedia transport and shown in FIG. 2. An edge guide in which the media ispushed laterally so that an edge of the media contacts a stop isprovided at A. The slack web entering the edge guide shifts the printmedia laterally without interference and without overconstraining theprint media. An S-wrap device SW provides stationary curved surfacesover which the continuous web slides during transport. As the paper ispulled over these surfaces the friction of the paper across thesesurfaces produces tension in the print media. In one embodiment, thisdevice helps to adjust the positional relationship between surfaces, tocontrol the angle of wrap and adjust web tension.

TABLE 1 Roller Listing for FIG. 2 Media Handling Component Type ofComponent A Lateral constraint (edge guide) SW—S-Wrap Zero constraint(non-rotating support), Tensioning B Angular constraint (in-feed driveroller) C Zero constraint (Castered and Gimbaled Roller) D* Angularconstraint with hinge (Gimbaled Roller) E Angular constraint with hinge(Gimbaled Roller) F Angular constraint (Fixed Roller) G Zero constraint(Castered and Gimbaled Roller) H Angular constraint with hinge (GimbaledRoller) TB—TURNOVER Discussed in more detail below I Zero constraint(Castered and Gimbaled Roller) J* Angular constraint with hinge(Gimbaled Roller) K Angular constraint with hinge (Gimbaled Roller) LAngular constraint (Fixed Roller) M Zero constraint (Castered andGimbaled Roller) N Angular constraint (out-feed drive roller) O Zeroconstraint (Castered and Gimbaled Roller) P Angular constraint withhinge (Gimbaled Roller) Note: Asterisk (*) indicates locations of loadcells.

The first angular constraint is provided by in-feed drive roller B. Thisis a fixed roller that cooperates with a drive roller in the turnoversection and with an out-feed drive roller N in second module 40 in orderto move the web through the printing system with suitable tension in themovement direction (from left to right as shown in FIG. 2). The tensionprovided by the preceding S-wrap serves to hold the paper against thein-feed drive roll so that a nip roller is not required at the driveroller. Angular constraints at subsequent locations downstream along theweb are often provided by rollers that are gimbaled so as not to imposean angular constraint on the next downstream web span.

There is a single lateral constraint mechanism used at A. Here, at thebeginning of the media path, a single edge guide provides lateralconstraint that is sufficient for registering the continuous web ofprint media along the media path. It is significant that only onelateral constraint is actively applied throughout the media path, here,as an edge guide. However, given this lateral constraint and thefollowing angular constraint, the lateral constraint for each subsequentweb span is fixed. In one embodiment, a gentle additional force isapplied along the cross-track direction as an aid for urging the mediaedge against the edge guide at A. This force is often referred to as anesting force as the force helps cause the edge of the media to nestalongside the edge guide.

Angular constraints, rollers B, D, E, F, H, J, K, L, N, P, are Includedin printing system 10. Each angular constraint sets the angulartrajectory of the web as it moves along. However, the web is nototherwise steered in the embodiment shown.

Fixed rollers at F and L precede the printheads for each module,providing the desired angular constraint to the web in the print zone.These rollers provide a suitable location of mounting an encoder formonitoring the motion of the media through the printing system. Underthe printheads, the print media is supported by fixed non-rotatingsupports. These supports provide zero constraint to the web.

Roller G is a castered and gimbaled roller providing zero constraint.Castered and gimbaled rollers provide zero constraint along the webpath. These mechanisms are used, for example, near the input to eachmodule, making each module independent of angular constraints fromearlier mechanisms. Other types of mechanisms that provide zeroconstraint include stationary curved surfaces or castered rollers.

If the span between roller F and G is sufficiently long, the continuousweb can lack sufficient stiffness to cause castered roller G to alignproperly with the web. In such cases, roller G need not be castered.Because of the relative length to width ratio of the media in thesegment between F and G, the continuous web in that segment isconsidered to be non-stiff, showing some degree of compliance in thecross-track direction. As a result, an additional constraint is includedto exactly constrain that web segment. This is accomplished byeliminating the caster from roller G. Axially compliant rollers canalternately be used where cross-track constraint is undesirable.

A digital printing system 50 shown schematically in FIG. 3 has aconsiderably longer print path than that shown in FIG. 3, but providesthe same overall sequence of angular constraints, with the same overallseries of gimbaled, castered, and fixed rollers. Table 2 lists theroller arrangement used with the system of FIG. 3 in one embodiment.Brush bars, shown between rollers F and G and between L and M in FIG. 3,are non-rotating surfaces and thus apply no lateral or angularconstraint forces.

TABLE 2 Roller Listing for FIG. 3 Media Handling Component Type ofComponent A Lateral constraint (edge guide) SW—S-Wrap Zero constraint(non-rotating support) B Angular constraint (in-feed drive roller) CZero constraint (Castered and Gimbaled Roller) D* Angular constraintwith hinge (Gimbaled Roller) E Angular constraint with hinge (GimbaledRoller) F Angular constraint (Fixed Roller) G Angular constraint withhinge (Gimbaled Roller) H Angular constraint with hinge (GimbaledRoller) TB—TURNOVER Discussed in more detail below I Zero constraint(Castered and Gimbaled Roller) J* Angular constraint with hinge(Gimbaled Roller) K Angular constraint with hinge (Gimbaled Roller) LAngular constraint (Fixed Roller) M Angular constraint with hinge(Gimbaled Roller) N Angular constraint (out-feed drive roller) O Zeroconstraint (Castered and Gimbaled Roller) P Angular constraint withhinge (Gimbaled Roller) Note: Asterisk (*) indicates locations of loadcells.

Turnover mechanism (TB) 30 is shown as part of second module 40.Turnover mechanism TB can optionally be configured as a separate module,with its web media handling compatible with that of second module 40.The position of turnover mechanism TB is appropriately between printzones 54 for opposite sides of the media.

Load cells are provided in order to sense web tension at one or morepoints in the system. In the embodiments of FIGS. 2 (Table 1) and 3(Table 2), load cells are provided at gimbaled rollers D and J. Controllogic for the respective digital printing system 50 monitors load cellsignals at each location and, in response, makes any needed adjustmentin motor torque in order to maintain the proper level of tensionthroughout the system. For the embodiments of FIGS. 2 and 3, the pacingdrive component of the printing apparatus is the turnover module TB.There are two tension-setting mechanisms, one preceding and onefollowing turnover module TB. On the input side, load cell signals atroller D indicate tension of the web preceding turnover module TB;similarly, load cell signals at roller J indicate web tension on theoutput side, between turnover module TB and take-up roll 18. Controllogic for the appropriate in- and out-feed driver rollers at B and N,respectively, can be provided by an external computer or processor, notshown in the figures of this application. Optionally, an on-boardcontrol logic processor 90, such as a dedicated microprocessor or otherlogic circuit, is provided for maintaining control of web tension withineach tension-setting mechanism and for controlling other machineoperation and operator interface functions.

The tension in a module preceding the turn bar and a module followingthe turnover module TB can be independently controlled relative to eachother further enhancing the flexibility of the printing system. Toaccomplish this, a drive motor is included in the turnover module TB.Alternatively, a drive motor is appropriately located along the web pathso that tension within one module is independently controlled relativeto tension in another module.

The configurations of FIGS. 1 and 2 were described as including twomodules 20 and 40. In the FIG. 1 configuration, each module provided acomplete printing apparatus. However, the “modular” concept need not berestricted to apply to complete printers. For example, the configurationof FIG. 3 is considered as formed of as many as seven modules.

An entrance module 70 is the first module in sequence, following themedia supply roll, as was shown earlier with reference to FIG. 1.Entrance module 70 provides the edge guide A that positions the media inthe cross-track direction and provides the S-wrap SW or otherappropriate web tensioning mechanism. In the embodiment of FIG. 3,entrance module 70 provides the in-feed drive roller B that cooperateswith SW and other downstream drive rollers to maintain suitable tensionalong the web, as noted earlier. Rollers C, D, and E are also part ofentrance module 70 in the FIG. 3 embodiment.

A first printhead module 72 accepts the web media from entrance module70, with the given edge constraint, and applies an angular constraintwith fixed roller F. A series of stationary brush bars or, optionally,minimum-wrap rollers then transport the web along past a first series ofprintheads 16 with their supporting dryers and other components. Here,because of the considerable web length in the web segment beyond theangular constraint provided by roller F (that is, the distance betweenrollers F and G), that segment can exhibit flexibility in the crosstrack direction which is an additional degree of freedom that needs tobe constrained. Eliminating the expected caster of roller G provides theadditional constraint needed in that span.

An end feed module 74 provides an angular constraint to the incomingmedia from printhead module 72 by gimbaled roller H. Turnover module TBaccepts the incoming media from end feed module 74 and provides anangular constraint with its drive roller, as described previously.

A forward feed module 76 provides a web span corresponding to each ofits gimbaled rollers J and K. These rollers again provide angularconstraint only; the lateral constraint for web spans in module 76 isobtained from the edge of the incoming media itself.

A second printhead module 78 accepts the web media from forward feedmodule 76, with the given edge constraint, and applies an angularconstraint with fixed roller L. A series of stationary brush bars or,optionally, minimum-wrap rollers then feed the web along past a secondseries of printheads 16 with their supporting dryers and othercomponents. Here again, because of considerable web length in the websegment (that is, extending the distance between rollers L and M), thatsegment will exhibit flexibility in the cross track direction which isan additional degree of freedom that needs to be constrained,eliminating the expected caster of roller M provides the additionalconstraint needed in that span. When overhang is present in the web span(that is, extending the distance between rollers L and M), exactconstraint principles are sometimes difficult to apply successfully.Gimbaled roller M provides additional constraint over this long webspan.

An out feed module 80 provides an out-feed drive roller N that serves asangular constraint for the incoming web and cooperates with other driverollers and sensors along the web media path that maintain the desiredweb peed and tension. Optional rollers O and P (not shown in FIG. 3) arealso provided for directing the printed web media to an externalaccumulator or take-up roll.

Each module in this sequence provides a support structure and an inputand an output interface for kinematic connection with upstream ordownstream modules. With the exception of the first module in sequence,which provides the edge guide at A, each module uses one edge of theincoming web media as its “given” lateral constraint. The module thenprovides the needed angular constraint for the incoming media in orderto provide the needed exact constraint or kinematic connection of theweb media transport. It can be seen from this example that a number ofmodules can be linked together. For example, an additional module canalternately be added between any other of these modules in order toprovide a useful function for the printing process.

Module function is adaptable to the configuration of the completeprinting system. In many cases, rollers and components areinterchangeable, including rollers at the interface between modules,moved from one module to another depending on the printer configuration.Frames and other support structures for the different modules either usea standard design and dimensions or are designed differently accordingto the contemplated application. This also helps to simplify upgradesituations.

There are a number of ways to track web position in order to locate andposition inkjet dots or other marking that is made on the media. Avariety of encoding and sensing devices are used for this purpose alongwith the associated timing and synchronization logic, provided bycontrol logic processor 90 or by some other dedicated internal orexternal processor or computer workstation. Such encoders or sensingdevices are typically placed just upstream of the print zone containingthe one or more printheads, and are preferably placed on a fixed rollerso as to avoid interfering with self aligning characteristic of casteredor gimbaled rollers.

Sometimes an active steering mechanism is used within a web span, forexample, when the web span length of an overhang exceeds its width, sothat the web no longer has sufficient mechanical stiffness for exactconstraint techniques. This happens, for example, where there isconsiderable overhang along the web span, that is, length of the webextending beyond the angular constraint for the span. This is the casefor modules 72 and 78 in the embodiment described with respect to FIG.3. In such a case, a castered roller in the overhang section of the weboften no longer behave as a zero constraint, since some amount oflateral force from the web is needed in order to align the casteredroller mechanism to the angle of the web span. This under-constraintcondition, due to length of the overhang along this lengthy web span, iscorrected by application of an additional constraint.

Kinematic connection between modules 20 and 40 follows the same basicprinciples that are used for exact constraint within each web span. Thatis, cross-track or edge alignment is taken from the preceding module.Any attempt to re-register the media edge as it enters the next modulewould cause an overconstraint condition. Rather than attempting to steerthe continuously moving media through a rigid and possiblyover-constrained transport system, the media transport componentsself-align to the media, thereby providing acceptable registration athigh transport speeds and reducing the likelihood of damage to the mediaor misregistration of applied ink or other colorant to the media.

Where multiple modules are used, as was described with reference to theembodiment shown in FIG. 3, the system should include a master driveroller that is in control of web transport speed. Often multiple driverollers are used and help provide proper tension in the web transport(x) direction, such as by applying suitable levels of torque, forexample. In one embodiment, the turnover TB module drive roller acts asthe master drive roller. The in-feed drive roller at B in module 20adjusts its torque according to a load sensing mechanism or load cellthat senses web tension between the drive and in-feed rollers.Similarly, out-feed drive roller N is controlled in order to maintain adesired web tension within second module 40.

Referring to FIG. 4, the web position in the span containing theprintheads 16 and dryers 14 is defined by a lateral constraint in theform of an edge guide F located immediately before the print zone and anangular constraint, non-pivoting roller M, located immediately after theprint zone. With the media under tension as it wraps around the shoe ofthe edge guide F, the shoe is free to pivot. This ensures that the mediahas uniform tension across its width in the print zone. In thisembodiment, the shoe rotates about an axis at the center of the shoe andperpendicular to the plane of the web segment from F to M. This rotationorientation reduces variation in spacing between the media andprintheads 16 as shoe F pivots. When the media is not under tension asit passes over the edge guide, the edge guide shoe need not be free topivot.

This embodiment also has an edge guide A and a non-pivoting drive rollerB that establish an initial path for the media in the first span of themedia entering the printing system. The combination of the castered andgimbaled rollers C and E and the gimbaled roller D removes anoverconstraint condition that would have existed between the first mediaspan and the span across the print zone. Edge guide A helps to ensurethat the only minor shifting of the lateral position of the web isneeded at edge guide F. This allows the bias force needed to shift themedia to the edge stop to be kept to a minimum. With the media undertension as it passes edge guide F, the required bias force to shift themedia is greater than it would be if the media were not under tension.The constraints provided by each roller are listed in table 3.

TABLE 3 Roller Listing for FIG. 4 Media Handling Component Type ofComponent A Lateral Constraint (Edge Guide) SW—S-Wrap Zero Constraint(Non-Rotating Support), Tensioning B Angular Constraint (In-Feed DriveRoller) C Zero Constraint (Castered and Gimbaled Roller) D* AngularConstraint with Hinge (Gimbaled Roller) E Zero Constraint (Castered andGimbaled Roller) F Lateral Constraint (Edge Guide) Brush Bars ZeroConstraint (Non-Rotating Support) M Angular Constraint (Non-PivotingRoller) N Zero Constraint (Castered and Gimbaled Roller) O AngularConstraint (Out-Feed Drive Roller) P Zero Constraint (Castered andGimbaled Roller) Q Angular Constraint with Hinge (Gimbaled Roller) Note:Asterisk (*) Indicates Locations Of Load Cells.

In the embodiment of FIG. 4, the printing system doesn't comprisemultiple modules. The media transport components are secured to a singlesupport structure. Through the use of rollers that align to the web, itis not necessary to precisely align the rollers to each other in thissystem. This greatly reduces the assembly costs for the system. Asprecise alignments are not required, the support structure to which thevarious rollers and web guides are mounted doesn't need to be as stiffas prior art frames. This allows the mass of the support structure to begreatly reduced which reduces shipping and setup costs.

As described above, continuous web media transport within and betweenone, two, three, or more modules is accomplished by applying exactconstraint techniques. This flexibility allows a web transportarrangement that provides acceptable registration and repeatableperformance at high speeds commensurate with the requirements ofhigh-speed color inkjet printing. As has been shown, multiple modulescan be integrated to form a printing system, without the requirement forpainstaking alignment of rollers or other media handling components atthe interface between two modules.

It has been found that web transports systems as described abovemaintain effective control of the print media in the context of adigital print system where the selected portions of the print media aremoistened in the printing process. This is true even when the printmedia is prone to expanding in length and width and to becoming lessstiff when it is moistened, such as for cellulose based print mediamoistened by a water based ink. This enables the individual color planesof a multi-colored document to be printed with acceptable registrationto each other.

The digital printing systems having one or more printheads thatselectively moisten at least a portion of the print media as describedabove include a media transport system that serves as a supportstructure to guide the continuous web of print media. The supportstructure includes an edge guide or other mechanism that positions theprint media in the cross track direction. This first mechanism islocated upstream of the printheads of the digital printing system. Theprint media is pulled through the digital printing system by a drivenroller that is located downstream of the printheads. The systems alsoinclude a mechanism located upstream of printheads of the printingsystem for establishing and setting the tension of the print media.Typically it is also located downstream of the first mechanism used forpositioning the print media in the cross track direction. The transportsystem also includes a third mechanism to set an angular trajectory ofthe print media. This can be a fixed roller (for example, a non-pivotingroller) or a second edge guide. The printing system also includes aroller affixed to the support structure configured to align to the printmedia being guided through the printing system without necessarily beingaligned to another roller located upstream or downstream relative to theroller. The castered, gimbaled or castered and gimbaled rollers serve inthis manner.

As noted earlier, slack loops are not required between or withinmodules. Slack loops can be appropriate where the continuous web isinitially fed from a supply roll or as it is re-wound onto a take-uproll, as was described with reference to the printing apparatus of FIG.1.

This system is adaptable for a printing system of variable size andfacilitates straightforward reconfiguration of a system withoutrequiring precise adjustment and alignment of rollers and relatedhardware when modules are combined. By using exact constraintmechanisms, rollers can be mounted within the equipment frame orstructure using a reasonable amount of care in mechanical placement andseating within the frame, but without the need to individually align andadjust each roller along the path, as would be necessary when usingconventional paper guidance mechanisms. That is, roller alignment withrespect to either the media path or another roller located upstream ordownstream is not needed.

Referring to FIGS. 5-8, example embodiments of an apparatus for movingthe continuous web of print media 60 are shown. A roller 100, having anaxis of rotation 102, includes a pattern of recesses 104 and ridges 106positioned along the axis of rotation 102. Roller 100 is divided intosections including a first section 108, a second section 110, and athird section 112. The second section 110 is located between the firstsection 108 and the third section 112 when viewed along the axis ofrotation 102. Roller 100 includes a profile as viewed along the axis ofrotation 102 that is typically referred to as a concave profile. In thisprofile, the diameter 114 of the ridges 106 located in the first section108 of the roller 100 and the diameter 116 of ridges 106 located in thethird section 112 of the roller 100 are greater than the diameter 118 ofthe ridges 106 located in the second section 110 of the roller 100.

The concave profile of roller 100, created by ridges 106, causes theprint media 60 to contact different locations of roller 100 as the webof print media 60 wraps around a portion of roller 100. This allowscauses roller 100 to provide lateral forces on the web of print media 60that spread (or stretch) the print media 60 in the cross track directionof the printing system 10 (to left and to the right as shown in FIG. 5).This helps to compensate for cross track expansion of the print media 60caused by the absorption of water-based ink that is applied to the printmedia 60 in print zone 54. The surface finish and coefficient offriction of the ridges 106 of roller 100 can be selected to provideappropriate friction between print media 60 and roller 100 for the levelof in-track tension, tension in the direction of print media travel, andamount of wrap, referred to as wrap angle, of print media 60 aroundroller 100.

In contrast to a pattern of ridges and recesses that spiral around andalong a roller in a non-perpendicular fashion relative to the axis ofrotation of the roller, the edges 120, 122 of ridges 106 and the edges124, 126 of recesses 104 wrap directly around roller 100 in aperpendicular fashion relative to the axis of rotation 102 of roller100. This creates ridges 106 and recesses 104 of roller 100 that alsoextend (or wrap around) the circumference of roller 100 in aperpendicular fashion relative to the axis of rotation 102 roller 100.Ridges 106 and recesses 104 extend in periodic manner along the length128 of roller 100. Recesses 104 provide area for the expanded printmedia 60 to fit into as the print media 60 wraps around roller 100. Thisreduces the likelihood of the print media 60 wrinkling as the printmedia 60 wraps around roller 100 and moves through printing system 10.Preferably, the combination of in-track web tension and the wrap angleis sufficient to cause print media 60 to pull slightly into the recesses104 of roller 100. In some applications, the depth of recesses 104 issized so that the portions of the print media 60 pulled into therecesses 104 of roller 100 contact a lower surface 130 of roller 100which helps minimize print media 60 distortion as the print media ispulled into the recesses 104.

In FIG. 5, the pattern of recesses 104 and ridges 106 positioned alongthe axis of rotation 102 of roller 100 is an alternating pattern ofrecesses 104 and ridges 106. The ridges 106 have a uniform width 142 asviewed along the axis of rotation 102 of roller 100. The diameter ofeach ridge 106 increases in a stepwise manner as viewed from the secondsection 110 of roller 100 toward both the first section 108 of roller100 and the third section 112 of roller 100. Each recess 104 includes asurface 130 that is parallel to the axis of rotation 102 of roller 100.The depth 132 of each recess varies when viewed from the second section110 of roller 100 toward both the first section 108 of roller 100 andthe third section 112 of roller 100. The surfaces 134 of ridges 106 areparallel to the axis of rotation 102 of roller 100

In FIG. 6, the pattern of recesses 104 and ridges 106 positioned alongthe axis of rotation 102 of roller 100 is an alternating pattern ofrecesses 104 and ridges 106. The ridges 106 have a uniform width 142 asviewed along the axis of rotation 102 of roller 100. The diameter ofeach ridge 106 increases when viewed from the second section 110 ofroller 100 toward both the first section 108 of roller 100 and the thirdsection 112 of roller 100. Each recess 104 includes a lower surface 130that is parallel to the axis of rotation 102 of roller 100. The depth132 of each recess varies when viewed from the second section 110 ofroller 100 toward both the first section 108 of roller 100 and the thirdsection 112 of roller 100. The surfaces 134 of ridges 106 are angledrelative to the axis of rotation 102 of roller 100 and are configured tocreate a radius of curvature 136 as viewed from a plane perpendicular tothe axis of rotation of the roller. The radius of curvature 136 beginsat the outside edge 138 of the first section 108 of roller 100, extendsthrough the section 110 of roller 100, and ends at the outside edge 140of the third section 112 of roller 100.

In FIG. 7, the pattern of recesses 104 and ridges 106 positioned alongthe axis of rotation 102 of roller 100 is an alternating pattern ofrecesses 104 and ridges 106. The diameter of each ridge 106 increaseswhen viewed from the second section 110 of roller 100 toward both thefirst section 108 of roller 100 and the third section 112 of roller 100.Additionally, the width 142 of at least a portion of ridges 106 locatedin the first section 108 of roller 100 and the third section 112 ofroller 100 is greater than the width of ridges located in the secondsection 110 of roller 100. The increased width of the ribs toward eachend of the roller enhance the lateral forces to spread the print media,when compared to rollers having uniform rib width along the length ofthe roller. Each recess 104 includes a lower surface 130 that isparallel to the axis of rotation 102 of roller 100. The depth 132 ofeach recess varies when viewed from the second section 110 of roller 100toward both the first section 108 of roller 100 and the third section112 of roller 100. The surfaces 134 of ridges 106 are angled relative tothe axis of rotation 102 of roller 100 and are configured to create aradius of curvature 136 as viewed from a plane perpendicular to the axisof rotation of the roller. The radius of curvature 136 begins at theoutside edge 138 of the first section 108 of roller 100, extends throughthe section 110 of roller 100, and ends at the outside edge 140 of thethird section 112 of roller 100.

In FIG. 8, the pattern of recesses 104 and ridges 106 positioned alongthe axis of rotation 102 of roller 100 is an alternating pattern ofrecesses 104 and ridges 106. The ridges 106 have a uniform width 142 asviewed along the axis of rotation 102 of roller 100. The diameter ofeach ridge 106 increases in a stepwise manner as viewed from the secondsection 110 of roller 100 toward both the first section 108 of roller100 and the third section 112 of roller 100. Each ridge 106 includesrounded corners 144. These rounded corners reduce the stresses on printmedia moving over the roller near the edges of the ridges. Each recess104 includes a surface 130 that includes a radius of curvature 146relative to the axis of rotation 102 of roller 100. The depth 132 ofeach recess varies when viewed from the second section 110 of roller 100toward both the first section 108 of roller 100 and the third section112 of roller 100. The surfaces 134 of ridges 106 are parallel to theaxis of rotation 102 of roller 100. The pattern of ridges and recessesis symmetric about the center (represented by centerline 150) of theroller, so that left side of the roller is a mirror image of the rightside of the roller as viewed in FIG. 8.

Although certain aspects of the example embodiments of the web movingapparatus have been discussed with reference to individual figures ofFIGS. 5-8. It should be understood that these aspects areinterchangeable or combinable. For example, the width 142 of ridges 106located in the first section 108 of roller 100 and the third section 112of roller 100 can be greater than the width ridges located in the secondsection if the roller in the example embodiment described with referenceto FIG. 5. The embodiments described with reference to FIGS. 5-7 canhave recess 104 that include a surface 130 that includes a radius ofcurvature 146 relative to the axis of rotation 102 of roller 100. Theridges 106 described in these embodiments can include rounded corners144.

As shown in FIGS. 5-8, roller 100 is free to rotate about its axis ofrotation 102. Referring to FIG. 9, in other example embodiment, roller100 is a driven roller, for example, driven directly by a motor 152 orby using another conventional roller driving mechanism. A first niproller 154 is positioned to engage a first ridge 156 of the ridges 106of roller 100 and a second nip roller 158 is positioned to engage asecond ridge 160 of the ridges of the roller. Typically, the first ridge156 is located in the first section 108 of roller 100 and the secondridge 160 is located in the third section 112 of roller 100 to helpfacilitate print media movement and minimize potential wrinkling of theprint media. As shown in FIG. 9, first ridge 156 is a ridge locatedproximate to a first edge 162 of print media and second ridge 160 is aridge located proximate to a second edge 164 of print media, as viewedin a cross track direction. As described above, certain aspects of theexample embodiments of the web moving apparatus have been discussed withreference to individual figures of FIGS. 5-9. It should be understoodthat these aspects are interchangeable or combinable.

As shown in FIGS. 5-9, the width 148 of each recess 104 of roller 100 isuniform. In other example embodiments, the recess 104 width 148 canvary. Alternatively, the width 142 of ridges 106 as viewed along theaxis of rotation can vary. For example, the width of the ridges locatedproximate to a first edge and a second edge of print media, as viewed ina cross track direction, is different when compared to the width ofridges located in other areas of the print media. This is done so thatthe edges 162, 164 of the print media 60 are in contact with a ridge 106of roller 100. In applications that contemplate moving print media 60 ofvarious widths, wider ridges 156, 160 are located proximate to theanticipated edge 162, 164 locations for each of the anticipated printmedia 60 widths.

Referring back to FIGS. 1-8, after roller 100 has been provided, the webof print media 60 is caused to contact and wrap around a portion ofroller 100 as the web of print media 60 moves past roller 100.Typically, this is accomplished by appropriately positioning roller 100and print media web 60 relative to each other, for example, by locatingroller 100 in one or both of roller locations G or M as described above.When provided roller 100 freely rotates about its axis of rotation,movement of the web of print media is accomplished using a print mediadriving mechanism, for example, one of the driven rollers describedabove with reference to FIGS. 1-4.

When roller 100 is a driven roller, the web of print media 60 is alsocaused to contact and wrap around a portion of roller 100 as the web ofprint media 60 moves past roller 100. After first nip roller 154 ispositioned to engage first ridge 156 of ridges 106 of roller 100 andsecond nip roller 158 is positioned to engage second ridge 160 of ridges106 of roller 100, the web of print media 60 is caused to pass betweenfirst nip roller 154 and first ridge 156 and to pass between second niproller 158 and second ridge 160. Typically, this is accomplished byappropriately positioning roller 100, first nip roller 154, second niproller 158, and print media web 60 relative to each other, for example,by locating roller 100, first nip roller 154, and second nip roller 158,in one or both of roller locations G or M as described above. Movementof the web of print media 60 is accomplished by driving roller 100using, for example, a motor or another conventional roller drivingmechanism.

One or more of printheads 16 ejects ink selectively moisten at least aportion of the web of print media 60 as the web of print media 60 isguided through printing system 10. Roller 100 is positioned downstreamfrom the printhead 16. An optionally included dryer 14, positioneddownstream from the printhead and upstream from the roller, removesmoisture from the print media 60 as the print media 60 moves past dryer14.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

PARTS LIST

-   -   10. Printing system    -   12. Source roller    -   14. Dryer    -   16. Digital printhead    -   18. Take-up roll    -   20. Module    -   22. Cross-track positioning mechanism    -   24. Tensioning mechanism    -   26. Constraint structure    -   28. Support structure    -   30. Turnover mechanism    -   40. Module    -   48. Support structure    -   50. Digital printing system    -   52. Slack loop    -   54. Print zone    -   60. Web of print media    -   70. Entrance module    -   72. Printhead module    -   74. End feed module    -   76. Forward feed module    -   78. Printhead module    -   80. Out-feed module    -   90. Control logic processor    -   100. Roller    -   102. Axis of rotation    -   104. Recesses    -   106. Ridges    -   108. First section    -   110. Second section    -   112. Third section    -   120. Edges    -   122. Edges    -   124. Edges    -   126. Edges    -   128. Length    -   130. Surface    -   132. Depth    -   134. Surfaces    -   136. Curvature    -   138. Outside edge    -   140. Outside edge    -   142. Uniform width    -   144. Rounded corners    -   146. Curvature    -   148. Width    -   150. Centerline    -   152. Motor    -   154. First nip roller    -   156. First ridge    -   158. Second nip roller    -   160. Second ridge    -   162. First edge    -   164. Second edge    -   A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P. Rollers    -   SW. S-wrap    -   TB. Turnover module

1. An apparatus for moving a continuous web of print media comprising: aroller having an axis of rotation, the roller including a pattern ofrecesses and ridges positioned along the axis of rotation of the roller,the roller including a first section, a second section, and a thirdsection, the second section being located between the first section andthe third section as viewed along the axis of rotation, the rollerincluding a profile as viewed along the axis of rotation in which thediameter of the ridges located in the first section of the roller andthe diameter of ridges located in the third section of the roller aregreater than the diameter of the ridges located in the second section ofthe roller.
 2. The apparatus of claim 1, the pattern of recesses andridges positioned along the axis of rotation of the roller being analternating pattern of recesses and ridges positioned along the axis ofrotation of the roller.
 3. The apparatus of claim 1, the ridges having awidth as viewed along the axis of rotation, the width of each ridgebeing uniform.
 4. The apparatus of claim 1, each of the ridges having adiameter as viewed along the axis of rotation, each ridge diameterincreasing in a stepwise manner as viewed from the second section of theroller toward both the first section of the roller and the third sectionof the roller.
 5. The apparatus of claim 1, the ridges furthercomprising a radius of curvature as viewed from a plane perpendicular tothe axis of rotation of the roller.
 6. The apparatus of claim 1, theridges having a width as viewed along the axis of rotation, the width ofthe ridges located in the first section of the roller and the thirdsection of the roller being greater than the ridges located in thesecond section of the roller.
 7. The apparatus of claim 1, thecontinuous web of print media including a first edge and a second edge,the ridges having a width as viewed along the axis of rotation, thewidth of the ridges located proximate to the first edge and the secondedge of print media being different when compare to the width of ridgeslocated in other areas of the print media.
 8. The apparatus of claim 1,the ridges including rounded corners.
 9. The apparatus of claim 1, eachrecess including a surface that includes a radius of curvature.
 10. Theapparatus of claim 1, each recess including a surface that is parallelto the axis of rotation.
 11. The apparatus of claim 1, each recesshaving a depth that varies when viewed from the second section of theroller toward both the first section of the roller and the third sectionof the roller.
 12. The apparatus of claim 1, the roller being free torotate about its axis of rotation.
 13. The apparatus of claim 1, theroller being a driven roller, the apparatus further comprising: a firstnip roller positioned to engage a first ridge of the ridges of theroller; and a second nip roller positioned to engage a second ridge ofthe ridges of the roller.